The present invention relates generally to fluid coupling devices for coupling the ends of two fluid-carrying conduits, and, more particularly, to an improved zero-spill double ball valve powered emergency release coupling in which two fluid-carrying conduits, each having a ball or plug valve received therein, are prevented from being decoupled unless both ball or plug valves are moved to a closed position prior to decoupling.
Coupling devices utilizing rotary valve elements that move between open and closed positions to regulate fluid flow are generally known. A problem exists where, upon closing of the two valve elements in such a coupling prior to decoupling, a certain amount of fluid becomes trapped in the flow passage between the two valve elements. Upon separation of the coupling or conduit ends, the trapped fluid may leak into the environment. To address this problem, it is known to use complementary ball valve elements in which one of the valve elements has a concave recess extending radially inward from its outer surface which is adapted to receive a convex portion of the other ball valve when the coupling ends are joined. The use of such complementary valve elements requires, however, that the valve element having the concave recess is closed first, positioning the concave recess adjacent to the other valve element in order to receive the convex portion. If the coupling is disconnected prior to proper zero-spill positioning of the valve elements spilling may occur. Thus, when the need arises to quickly separate the zero-spill coupling in emergency situations, the coupling must be provided with fail-safe means for regulating the closing sequence of the valve elements prior to separation and for preventing disconnection of the coupling prior to zero-spill positioning of the valve elements.